What video standard did you shoot this to? You always have the option to expand what you didn’t cover by the garbage matte through the motion tab, but the downside is that it is only blowing up the video.
If you don’t want to do that, you can always go into powerpoint or something related. When you go into there, you could make a slide entirely a saturated green or blue. Then save it as a jpeg or what have you, import it, and put the picture into your first video track. Put the track you are matting on track 2. Then key each of them separately.
I use this convoluted method quite often – though I haven’t keyed two different colors. What I suggested is theoretically possible, but I won’t guarantee anything. Hope your problem gets worked out.